Supattapone et al. reported that a polypeptide having IP3 binding activity was purified from the rat cerebellum [Surachai Supattapone et al, Journal of Biological Chemistry, 263, 1530 (1988)]. The amino acid sequence of this polypeptide is not specified, however. Nordquist et al. cloned randomly three clones of complementary DNA (hereinafter referred to as "cDNA") specific to the mouse cerebellum [Daniel T. Nordquist et al., The Journal of Neuroscience, 8, 4780 (1988)]. Although one of them has a high level of homology to a DNA fragment according to the invention, no mention has been made of the polypeptide encoded by this cDNA having the ability to bind to IP3. This cDNA constitutes only a part of the DNA according to the invention. Maeda et al. purified a glycoprotein, P400, occurring specifically in mouse cerebellum Purkinje cells and having a molecular weight of 250 kilodaltons (Kd). They failed, however, to show that the protein was able to bind to IP3 [N. Maeda et al., Journal of Neurochemistry, 51, 1724 (1988)]. Previously, neither production, by means of recombinant DNA techniques, of a polypeptide capable of binding to IP3 nor determination of the primary sequence of such polypeptide or a gene coding therefor through analysis of such a gene has been reported.